﻿620 
  Dr. 
  J. 
  A. 
  Gray 
  on 
  the 
  Scattering 
  and 
  

  

  reduced 
  from 
  5*40 
  to 
  1*91, 
  or 
  to 
  35 
  per 
  cent., 
  while 
  the 
  

   intensity 
  of 
  the 
  primary 
  radiation 
  falls 
  to 
  42 
  per 
  cent. 
  

   Similar 
  results 
  are 
  to 
  be 
  obtained 
  from 
  Table 
  II. 
  In 
  the 
  

   case 
  of 
  the 
  scattered 
  radiation 
  from 
  lead 
  the 
  much 
  greater 
  

   absorption 
  of 
  the 
  softer 
  rays, 
  both 
  primary 
  and 
  scattered, 
  

   vitiates 
  this 
  comparison. 
  

  

  The 
  fact 
  that 
  softer 
  rays 
  are 
  scattered 
  to 
  a 
  greater 
  extent 
  

   is, 
  of 
  course, 
  to 
  be 
  expected. 
  In 
  a 
  previous 
  paper 
  the 
  writer 
  

   introduced 
  a 
  coefficient 
  Sj/p, 
  &idx 
  representing 
  the 
  intensity 
  

   of 
  the 
  radiation 
  scattered 
  for 
  a 
  parallel 
  beam 
  between 
  the 
  

   angles 
  90° 
  and 
  270°. 
  

  

  In 
  the 
  case 
  of 
  X 
  rays 
  Si/p 
  is 
  of 
  the 
  order 
  O'lOO. 
  

  

  In 
  the 
  case 
  of 
  7 
  rays 
  of 
  radium 
  E 
  Sj/p 
  is 
  of 
  the 
  order 
  0*050. 
  

   In 
  the 
  present 
  case 
  a 
  special 
  experiment 
  showed 
  that 
  a 
  carbon 
  

   radiator 
  reflects 
  about 
  12 
  per 
  cent, 
  of 
  the 
  7 
  rays 
  of 
  radium 
  E, 
  

   and 
  it 
  is 
  easy 
  to 
  prove 
  that 
  if 
  fju 
  represents 
  the 
  absorption 
  

   coefficient 
  of 
  the 
  primary 
  rays 
  in 
  carbon, 
  \ 
  the 
  absorption 
  

   coefficient 
  of 
  the 
  reflected 
  rays, 
  and 
  P 
  the 
  fraction 
  of 
  rays 
  

   reflected, 
  

  

  S 
  1 
  //) 
  = 
  P( 
  A 
  6 
  + 
  X)/p. 
  

  

  For 
  carbon, 
  yu/p 
  = 
  0'044, 
  A/p 
  = 
  0'080, 
  P 
  = 
  0'12, 
  

  

  and 
  S 
  1 
  /p 
  = 
  0*015, 
  

  

  showing 
  that 
  the 
  scattering 
  decreases 
  as 
  the 
  rays 
  become 
  

   harder. 
  

  

  The 
  numbers, 
  although 
  approximate, 
  are 
  sufficiently 
  accurate 
  

   to 
  show 
  that 
  the 
  scattering 
  of 
  7 
  rays 
  is 
  quite 
  marked 
  in 
  com- 
  

   parison 
  with 
  direct 
  absorption. 
  For 
  this 
  reason 
  it 
  is 
  practi- 
  

   cally 
  impossible 
  to 
  separate 
  the 
  primary 
  and 
  scattered 
  rays, 
  

   and 
  these 
  scattered 
  rays 
  play 
  a 
  great 
  part 
  in 
  absorption 
  

   phenomena. 
  

  

  Absorption 
  of 
  7 
  Rays. 
  

  

  When 
  examined 
  by 
  most 
  materials, 
  the 
  7 
  rays 
  of 
  radium 
  

   become 
  more 
  and 
  more 
  penetrating, 
  this 
  being 
  particularly 
  

   marked 
  in 
  the 
  case 
  of 
  absorption 
  by 
  lead 
  and 
  other 
  substances 
  

   of 
  high 
  atomic 
  weight. 
  After 
  passing 
  through 
  a 
  certain 
  

   amount 
  of 
  any 
  material 
  the 
  absorption 
  becomes 
  exponential, 
  

   Russell 
  * 
  finding 
  that 
  the 
  absorption 
  in 
  mercury 
  is 
  expo- 
  

   nential 
  for 
  a 
  thickness 
  of 
  1 
  cm. 
  to 
  22*5 
  cm., 
  the 
  intensity 
  

   diminishing 
  in 
  the 
  ratio 
  360,000 
  to 
  1. 
  

  

  The 
  tables 
  show 
  us 
  that 
  even 
  though 
  the 
  absorption 
  is 
  

   exponential, 
  the 
  rays 
  are 
  not 
  homogeneous 
  owing 
  to 
  scattered 
  

  

  * 
  Russell, 
  Proc. 
  Roy. 
  Soc. 
  A, 
  Isxxvii. 
  (1912). 
  

  

  